Year: 2026
Type: preprint
Abstract: Cosmic birefringence, the rotation of the polarization plane of cosmic microwave background (CMB) photons, provides an intriguing probe of physics beyond the Standard Model. In this paper, we investigate a vector Chern-Simons coupling between the neutrino current and photons as a possible origin of isotropic cosmic birefringence. Firstly, we perform the first analysis of anisotropic cosmic birefringence induced by the neutrino current. We find that the anisotropic signal sourced by lepton-number isocurvature fluctuations can be important on large scales, whereas on small scales, the anisotropic signal induced by gravitational effects becomes dominant comparing with the axion-like particle (ALP) scenario. Secondly, we show that a large lepton asymmetry generated through the Affleck-Dine mechanism can successfully account for the observed isotropic birefringence, and discuss its possible connection to the recently reported low helium-4 abundances in Subaru EMPRESS and Atacama Cosmology Telescope (ACT).
Source: arXiv (Cornell University)
Authors: Kasai, Kentaro, Obata, Ippei
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7220901506